The present invention relates to an odor measuring apparatus for measuring and analyzing odors (flavor, fragrance, stench, etc.), which is used for identifying an unknown odor and for measuring its odor intensity. The present invention is applicable to various fields of apparatus such as one for measuring stenches or an apparatus for inspecting and/or evaluating the quality of foodstuffs or medicines.
Conventionally, the discernment and evaluation of odors is performed by the olfactory sense of the human being. By this method, it must be considered that different persons (or panels) have different olfactory sensitivities and the olfactory sense of a panel may vary depending on such mitigating factors as mood, alertness, health, etc. of the panel, or on the day of the test. Therefore, to obtain an objective result with high systematic accuracy, it is necessary to gather an adequate number of panels and to conduct the test under an adequately uniform environmental condition. Thus, the test often consumes a lot of time and labor. Further, even under a desirable physical and environmental condition, it is very difficult to obtain a conclusive result based on a fixed standard because the olfactory sense of the human being easily adapts to odor.
One solution to this problem is a flavor and fragrance analyzer as disclosed in the Japanese Unexamined Patent Publication No. H11-352088, an example of which is xe2x80x9cFF-1xe2x80x9d commercially manufactured by Shimadzu Corporation. The flavor and fragrance analyzer, which has plural odor sensors, calculates the distance (or similarity) between the odors of plural samples based on the detection signals of the odor sensors. The calculation is performed, for example, by multivariate analysis such as cluster analysis or principal component analysis, or by a nonlinear analysis using a neural network.
The above flavor and fragrance analyzer is particularly applicable to the inspection of the quality of foodstuffs, or other analyses where the similarity of plural odors shall be relatively determined within a comparatively narrow range of categories. This analyzer, however, has the following problems:
(1) It is difficult to objectively or absolutely determine the similarity of a wide range of odors, as in the case of the examination of bad odors.
(2) Since the sensitivity of the odor sensor is not always consistent with that of the human nose, the result obtained by the analyzer sometimes differs from that obtained by the organoleptic examination by the olfactory sense.
(3) It is difficult to visually understand the similarity between an odor and plural standard odors.
(4) Even when two odors are discernable, it is often difficult to definitely determine whether they differ in odor intensity or in odor quality.
To solve the above problems, one object of the present invention is to propose an odor measuring apparatus capable of showing the similarity of a various kinds of odors to known standard odors by absolute values. Another object is to propose an odor measuring apparatus capable of discriminating odors like the olfactory sense of the human being.
Thus, the present invention proposes a first odor measuring apparatus, which includes:
a) m pieces of odor sensors having different responsive characteristics, where m is an integer greater than one (i.e., two or more);
b) an angle calculator for calculating the angle between an unknown odor vector and a standard odor vector in an m-dimensional space formed by the result of a measurement with the m pieces of odor sensors, where the unknown odor vector is represented by the result of a measurement of an unknown sample and the standard odor vector is represented by the result of a measurement of a known standard odor; and
c) an index calculator for calculating an index which represents a similarity of the unknown odor to the standard odor, where the index is calculated based on the angle.
In the measurement of a standard odor with the m pieces of odor sensors, every odor sensor produces an intensity signal, so that m pieces of data are obtained. Mathematically, the m pieces of data can be represented by a point in an m-dimensional space (xe2x80x9csensor""s odor spacexe2x80x9d). When plural standard samples containing the standard odor of different concentrations are measured, the point moves within the sensor""s odor space in a certain direction with the change of the concentration. The movement of the point can be defined by a vector called xe2x80x9codor vectorxe2x80x9d in this specification. The odor vector is specific to the kind of the odor concerned. Therefore, in the sensor""s odor space, when the direction of the odor vector obtained by a measurement of a sample containing an unknown odor is close to that of the standard odor vector, the two odors can be determined as similar kinds. In contrast, when the directions of the two odor vectors differs greatly, the two odors are determined as distant kinds.
Thus, in the first odor measuring apparatus, the angle calculator calculates the angle between the standard odor vector and the unknown odor vector as an index for representing the distance between the two vectors. Then, using the angle as the basis, the index calculator calculates an index to be used for determining the similarity of the odor of the unknown sample to the standard odor. For example, the index is determined as a percentage of similarity ranging from 0 to 100%. When the angle is zero, the standard odor and the odor of the unknown sample can be regarded as the same kind, and the percentage of similarity is determined as 100%. When the angle is greater than a preset angle, the standard odor and the odor of the unknown sample are regarded as being totally different kinds, and the degree of similarity is determined as 0%.
Thus, the first odor measuring apparatus can show the similarity of an unknown odor to a standard odor by an absolute value. Therefore, odors can be discriminated more objectively than before, and it is easier to compare plural unknown odors and determine their similarity. Proper selection of plural kinds of standard odors will make it possible to obtain the similarity of an unknown odor to each of the standard odors. Thus, various kinds of odors can be discriminated with adequate accuracy, so that the apparatus can be applied to various fields.
The first odor measuring apparatus may further include an intensity calculator for calculating an index relating to an odor intensity by a method including the following steps: taking the orthogonal projection of the unknown odor vector on the standard odor vector; deriving the odor concentration of the standard odor vector component of the unknown sample from the length of the orthogonal projection of the unknown odor vector; and calculating the index relating to the odor intensity. Such a construction makes it possible to obtain not only the similarity of the odor of an unknown sample to the standard odor but also the odor intensity, odor index or the like.
In a preferable mode of the invention, the index calculator includes a corrector for correcting the index, taking account of the difference in sensitivity between the odor sensor and the olfactory sense of the human being. Such a construction makes the measurement result free from the influence due to the difference in the sensitivity between the odor sensor and the olfactory sense of the human being, where the result becomes more natural to the sense of the human being. Thus, the apparatus according to the present invention becomes more suitable as an alternative to organoleptic examination.
Further, the first apparatus may include a storage unit for pre-storing results of measurements of n kinds of standard odors by the odor sensors, where n is an integer greater than one (i.e., two or more), or for pre-storing standard odor vectors represented by the results of the measurements.
By this construction, plural kinds of standard odors are measured beforehand, and the results of the measurements are stored in the storage unit. After that, a measurement of only an unknown sample is necessary to objectively discriminate or evaluate the odor of the unknown sample. In particular, the odor of an unknown sample can be properly indicated by plural indices of similarity. Further, the apparatus may include a display for visually showing the plural indices of similarity. This construction helps an intuitive understanding of the result of the measurement, so that even those who are not skilled in odor analysis can use the apparatus without difficulty.
The present invention further proposes a second odor measuring apparatus which includes:
a) m pieces of odor sensors having different responsive characteristics, where m is an integer greater than one (i.e., two or more);
b) a concentration point locator for locating a temporary point of concentration on a standard odor curve in an m-dimensional space formed by the result of measurement with the m pieces of odor sensors, where the standard odor curve is represented by the result of a measurement of a known standard odor, and the temporary point of concentration is located by a preset rule with respect to a measurement point representing the result of a measurement of an unknown sample; and
c) an index calculator for calculating an index representing the similarity of the unknown odor to the standard odor, where the index is calculated based on the location of the temporary point of concentration in the m-dimensional space and on a value representing an index of proximity of the temporary point of concentration to the measurement point.
When plural standard samples with different concentrations of the same standard odor are measured, the measurement points of these samples are located apart from each other due to the difference in the concentration of the standard odor. These measurement points form a curve (or a straight line in some cases) corresponding to the standard odor. The points on this curve (called the xe2x80x9cstandard odor curvexe2x80x9d in this specification) correspond to different concentrations of the standard odor.
In the second apparatus, the concentration point locator follows a preset rule to locate a temporary point of concentration on the standard odor curve corresponding to the measurement point representing the result of the measurement of an unknown sample. The temporary point of concentration can be regarded as indicative of the concentration of the odor measured on the assumption that the odor of the unknown sample contains only the standard odor. When the measurement point of the unknown sample is not located on the standard odor curve, the degree of contribution of the standard odor to the odor of the unknown sample can be regarded to depend on the proximity of the measurement point to the temporary point of concentration within the space. Thus, the index calculator estimates the odor concentration from the location in the space of the temporary point of concentration and the degree of contribution of the standard odor from the index of proximity, and then calculates the index for determining the similarity of the unknown odor to the standard odor.
Thus, the second odor measuring apparatus can show the similarity of an unknown odor to a standard odor by an absolute value. Therefore, odors can be discriminated more objectively than before, and it is easier to compare plural unknown odors and determine their similarity. Proper selection of plural kinds of standard odors will make it possible to obtain the similarity of an unknown odor to each of the standard odors. Thus, various kinds of odors can be discriminated with adequate accuracy, so that the apparatus can be applied to various fields.
In a mode of the present invention, the concentration point locator locates the temporary point of concentration as the point on the standard odor curve where the distance from the measurement point is minimized. The index calculator attenuates the concentration, derived from the location in the space of the temporary point of concentration, according to the distance between the temporary point of concentration and the measurement point, or according to the angle between a standard odor line and an unknown odor line drawn on the assumption that each of the standard odor and the unknown odor changes along a straight line with respect to concentration. The index calculator then calculates the index regarding the attenuated concentration as indicative of the contribution of the standard odor to the odor of the unknown sample.
The above distance changes with the odor intensity even when the odor is of the same kind. Therefore, when the degree of attenuation is determined based on the distance, it is preferable to reduce the influence of the odor intensity by, for example, correcting the distance considering the odor intensity.
The index calculator may preferably include a corrector for performing a correction taking account of the difference in sensitivity between the odor sensor and the olfactory sense of the human being, using the threshold of the olfactory sense of the human being. This construction makes the result of the measurement or discernment of an odor consistent with the olfactory sense of the human being.
Similar to the first apparatus, the second apparatus may further include a storage unit for pre-storing the results of measurements of n kinds of standard odors by the odor sensors, where n is an integer greater than one, or for pre-storing standard odor vectors represented by the results of the measurements. This construction provides the same effect as described above regarding the storage unit of the first odor measuring apparatus.
By a further preferable construction, the storage unit stores the standard odor curve in association with information about the measurement date of the standard odor, and the concentration point locator locates the temporary point of concentration on the standard odor curve by using a standard odor curve of the latest measurement date. By this construction, the accuracy of the measurement is improved in the case where several kinds of standard odors are used because the latest results of the measurements of the standard odors can be always used for a measurement of an unknown sample even when the measurements of the standard odors are not conducted continuously or on the same day.